As one example of a method for forming a film on a substrate, a plasma enhanced atomic layer deposition (PE-ALD) method has been used. In the PE-ALD method, a substrate is exposed to a precursor gas, whereby the precursor gas which contains a constituent element of a thin film to be formed is chemisorbed onto the substrate. Subsequently, the substrate is exposed to a purge gas, thereby removing the precursor gas excessively chemisorbed onto the substrate. Then, the substrate is exposed to plasma of a reaction gas which contains a constituent element of a film to be formed, consequently forming a desired thin film on the substrate. In the PE-ALD method, this process is repeated such that a film obtained by processing atoms or molecules contained in the precursor gas is formed on the substrate.
As an apparatus for implementing the PE-ALD method, a semi-batch type film forming apparatus has been used. In the semi-batch type film forming apparatus, a region to which the precursor gas is supplied and a region in which the plasma of the reaction gas is generated, are independently provided within a process chamber. The substrate passes through these regions in the order named. As a result, a desired film is formed on the substrate.
In the aforementioned PE-ALD method, film quality is improved if a modifying process performed using plasma of a modifying gas such as hydrogen or the like is added after the adsorption process performed using the precursor gas or after the reaction process performed using the plasma of the reaction gas.
In the semi-batch type film forming apparatus, when performing the modifying process after the adsorption process or the reaction process, it is thinkable that, in addition to an adsorption process region and a reaction process region, a modifying process region is formed within the process chamber. However, in this case, it is necessary to independently control the gases in a region where the plasma of the reaction gas is generated and in a region where the plasma of the modifying gas is generated. This poses a drawback in that the cost of the substrate processing apparatus becomes higher. Furthermore, the gases are mixed in a region between the region where the plasma of the reaction gas is generated and the region where the plasma of the modifying gas is generated. This leads to deterioration of the processing uniformity and the film quality.